The apparatus of Applicant's prior U.S. Pat. No. 3,779,182 includes a furnace chamber containing mixed refuse that is heated by plasma torches. The plasma torches are disposed above a hearth of the furnace chamber, and above the mass of refuse extending upwardly from such hearth. This results in part of the heat generated by the torches not being utilized to its maximum extent, since the heat ascends to the top of the chamber without passing through any of the refuse within the lower part of the furnace chamber.